Method of manufacturing oxide superconducting wire, oxide superconducting wire, superconducting coil and superconducting apparatus

ABSTRACT

A method of manufacturing an oxide superconducting wire which can manufacture the longest possible wire by connecting relatively short wires with each other and is capable of suppressing reduction of a critical current resulting from influence by strain when the wires connected with each other are bent, an oxide superconducting wire, a superconducting coil and a superconducting apparatus are provided. According to the method of manufacturing an oxide superconducting wire by superposing end portions of two oxide superconducting wires ( 1, 2 ) with each other thereby bonding the end portions and connecting the oxide superconducting wires with each other, a junction (L) formed by superposing the end portions with each other is so worked as to reduce the quantity of strain on an end of the junction (L) when the two oxide superconducting wires ( 1 ) and ( 2 ) connected with each other are bent. Each of the oxide superconducting wire, the superconducting coil and the superconducting apparatus has the aforementioned junction (L), and the quantity of strain on the end of the junction (L) is reduced in the aforementioned manner.

TECHNICAL FIELD

The present invention relates to a method of manufacturing an oxidesuperconducting wire, an oxide superconducting wire, a superconductingcoil and a superconducting apparatus, and more particularly, it relatesto superconducting apparatuses such as a superconducting transformer, asuperconducting current limiter and a magnetic field generator employingsuperconducting magnets prepared from oxide superconducting wires, asuperconducting cable and a superconducting bus bar employing oxidesuperconducting wires and the like and a method of manufacturing anoxide superconducting wire applicable for manufacturing thesesuperconducting apparatuses.

BACKGROUND TECHNIQUE

In general, a sufficient length is required for an oxide superconductingwire employed in a practical superconducting apparatus. In order tomanufacture a cable conductor having a capacity of at least 100megawatts (MW) as a practical superconducting cable, for example,hundreds of oxide superconducting wires exhibiting a unit length ofabout 5 km as the final length of the superconducting cable arerequired. In this case, a wire (diameter: 0.9 mm, critical current: 20A, temperature: 77 K) formed by bismuth oxide superconductor filamentscoated with silver is employed as the oxide superconducting wire, forexample.

As a superconducting magnet employed for a magnetic separator or amagnetic field generator, a magnet having an inner diameter exceeding 1m is manufactured. In order to manufacture such a superconductingmagnet, about 1000 oxide superconducting wires exhibiting a unit lengthof about 800 m per coil are required, for example. In this case, atape-like wire (thickness: 0.25 mm, width: 4 mm, critical current: 50 A(temperature: 77 K)) formed by bismuth oxide superconductor filamentscoated with silver is employed as the oxide superconducting wire.

At the current level of the technique of manufacturing an oxidesuperconducting wire, however, only a wire formed by bismuth oxidesuperconductor filaments coated with silver having a unit length ofabout several 100 m is manufactured. When the oxide superconducting wireof such a unit length has a single defective portion, the entire oxidesuperconducting wire of about several 100 m is regarded as defective, todisadvantageously result in a low manufacturing yield. Unless atechnique of manufacturing an elongated oxide superconducting wire isdeveloped, therefore, it is impossible at present to apply the currenttechnique to the aforementioned practical superconducting apparatus.This is one of the primary factors for delay in the application ofsuperconducting apparatus, which is an innovative technique, to industryand practical application thereof.

If a wire having a large unit length can be manufactured by connectingrelatively short oxide superconducting wires with each other in order toimplement the aforementioned superconducting cable having a capacity ofat least 100 MW or a superconducting magnet employed for a magneticfield generator, it is possible to prepare a prototype apparatus forapplying a superconducting apparatus to industry. Further, it ispossible to understand the merits of the superconducting apparatusthrough the prepared prototype apparatus for progress in practicalapplication.

However, the critical current of an oxide superconducting wire isdisadvantageously reduced due to influence by strain resulting fromdeformation such as bending or tension. When end portions of oxidesuperconducting wires having a small unit length are superposed forconnecting the oxide superconducting wires with each other by brazing orsoldering, for example, the wires are bent through a guide roller or thelike in the process of manufacturing a superconducting cable or asuperconducting magnet and the critical current is reduced due tobending strain applied to the wires. This is because the junction formedby superposing the end portions with each other is hardly bent while theremaining portions are readily bent. Hence an end of the junction isbent with a bending radius smaller than the radius of the guide rolleror the like when the end of the junction is bent through the guideroller or the like. As a result, a strain larger than an allowablebending strain for allowing the wires to maintain the critical currentis applied to the end of the junction. Even if an oxide superconductingwire having a large unit length can be obtained by connecting the wires,therefore, the critical current is reduced due to influence by thestrain applied to the end of the junction of the wire and hence it isdisadvantageously difficult for a practical superconducting apparatusformed by the long wire to attain a prescribed function.

Accordingly, an object of the present invention is to provide a methodof manufacturing an oxide superconducting wire which can manufacture thelongest possible wire by connecting relatively short wires with eachother and is capable of suppressing reduction of a critical currentresulting from influence by strain also when the wire is bent afterconnection.

Another object of the present invention is to provide an oxidesuperconducting wire, a superconducting coil and a superconductingapparatus each comprising a connected portion, which can suppressreduction of an initial critical current of wires before connection alsoin a bent state.

DISCLOSURE OF THE INVENTION

A method of manufacturing an oxide superconducting wire according to anaspect of the present invention comprises a step of bonding end portionsof two oxide superconducting wires by superposing the end portions witheach other for connecting the oxide superconducting wires with eachother and a step of working a junction formed by superposing the endportions with each other to reduce the quantity of strain on an end ofthe junction to be close to the quantity of strain on non-superposedportions of the oxide superconducting wires when the two oxidesuperconducting wires connected with each other are bent.

When the junction is worked in the aforementioned manner, reduction of acritical current caused by bending strain can be suppressed also whenthe wire is bent through a guide roller or the like after connection.Therefore, an oxide superconducting wire having a length necessary forvarious superconducting apparatuses can be prepared by connectingrelatively short oxide superconducting wires. Also when such a longoxide superconducting wire is left in a state wound on a reel or thelike, reduction of the critical current caused by applied strain issuppressed. Therefore, a long superconducting cable or a largesuperconducting magnet can be manufactured by continuously supplying theprepared long oxide superconducting wire while simultaneously performinginsulating coating on the wire.

In the method of manufacturing an oxide superconducting wire accordingto the present invention, the step of bonding the aforementioned oxidesuperconducting wires is preferably carried out by superposing the endportions of the two oxide superconducting wires with each other withinterposition of a brazing filler metal.

The oxide superconducting wires are preferably tape-like wires havingrectangular cross sections.

The step of bonding the aforementioned oxide superconducting wires ispreferably carried out by superposing wide surfaces of two tape-likewires with each other. The aforementioned step of working theaforementioned junction is preferably carried out by working the endportions so that the widths of the tape-like members are reduced towardthe ends.

The step of working the aforementioned junction is preferably carriedout by cutting the end portions to have V shapes in plane or by cuttingthe end portions so that the end portions have end surfaces inclined inthe width direction across the widths of the tape-like wires.

The step of working the aforementioned junction is preferably carriedout by working the end portions so that the thicknesses of the tape-likewires are reduced toward the ends.

The oxide superconducting wires may be round wires.

Further, the step of working the aforementioned junction is preferablycarried out by at least partially coating the junction with a metal oran organic substance thereby reducing the aforementioned quantity ofstrain. In this case, the step of working the aforementioned junction ispreferably carried out by at least partially inserting the junction intoa material having an annular shape.

The oxide superconducting wire to which the manufacturing methodaccording to the present invention is applied preferably contains abismuth oxide superconductor. When the bismuth oxide superconductor isemployed, the wire is preferably formed by bismuth oxide superconductorfilaments coated with a material containing silver.

An oxide superconducting wire according to another aspect of the presentinvention comprises a first oxide superconducting wire having an endportion, a second oxide superconducting wire having an end portion and ajunction formed by superposing the end portions of the first and secondoxide superconducting wires with each other, and the quantity of strainon an end of the junction is reduced to be close to the quantity ofstrain on non-superposed portions of the first and second oxidesuperconducting wires.

When the oxide superconducting wire having the aforementioned structureis employed, reduction of initial critical currents of the wires beforeconnection can be suppressed also when the wires are bent through aguide roller or the like in the process of manufacturing asuperconducting cable or a superconducting magnet. Therefore, reductionof a yield can be suppressed when manufacturing a final superconductingcable or superconducting magnet by employing the oxide superconductingwire according to the present invention, while a long superconductingcable or a large superconducting magnet can be manufactured with highproductivity.

In the oxide superconducting wire according to the present invention,the junction preferably includes a brazing filler metal interposedbetween the superposed end portions of the first and second oxidesuperconducting wires.

The oxide superconducting wires are preferably tape-like wires havingrectangular cross sections.

The junction preferably includes a junction formed by superposing widesurfaces of two tape-like wires. The junction preferably includes an endportion so worked that the widths of the tape-like wires are reducedtoward the end.

Further, the junction preferably includes an end portion having a Vshape in plane or an end portion having an end surface inclined in thewidth direction across the widths of the tape-like wires.

The junction preferably includes an end portion so worked that thethicknesses of the tape-like wires are reduced toward the end.

The oxide superconducting wires may be round wires.

Further, the junction is preferably at least partially coated with ametal or an organic substance. In this case, the junction is preferablyat least partially inserted into a material having an annular shape.

The oxide superconducting wires preferably contain a bismuth oxidesuperconductor. The bismuth oxide superconductor is preferably afilament coated with a material containing silver.

A superconducting coil according to still another aspect of the presentinvention comprises a first oxide superconducting wire having an endportion, a second oxide superconducting wire having an end portion and ajunction formed by superposing the end portions of the first and secondoxide superconducting wires with each other, and the quantity of strainon an end of the junction is reduced to be dose to the quantity ofstrain on non-superposed portions of the first and second oxidesuperconducting wires.

A superconducting apparatus according to a further aspect of the presentinvention comprises a first oxide superconducting wire having an endportion, a second oxide superconducting wire having an end portion and ajunction formed by superposing the end portions of the first and secondoxide superconducting wires with each other, and the quantity of strainon an end of the junction is reduced to be close to the quantity ofstrain on non-superposed portions of the first and second oxidesuperconducting wires.

According to the present invention, as hereinabove described, thelongest possible wire can be manufactured by connecting short wireswhile reduction of a critical current resulting from influence bybending strain can be effectively suppressed by working the junction toreduce the quantity of strain on the end of the junction when theconnected oxide superconducting wires are bent. Therefore, a long oxidesuperconducting wire used for a long superconducting cable or a largesuperconducting magnet can be previously prepared in a state suppressingreduction of the critical current. Thus, the oxide superconducting wirecan be manufactured with high productivity without reducing amanufacturing yield. Consequently, the oxide superconducting wire or thesuperconducting coil according to the present invention can be appliedto various superconducting apparatuses for readily progressing practicalapplication.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view schematically showing anembodiment (1) of a method or a mode of connecting oxide superconductingwires according to the present invention.

FIG. 2 is a longitudinal sectional view schematically showing anembodiment (7) of the method or the mode of connecting oxidesuperconducting wires according to the present invention.

FIG. 3 is a longitudinal sectional view schematically showing anembodiment (7) of the method or the mode of connecting oxidesuperconducting wires according to the present invention.

FIG. 4 is a longitudinal sectional view schematically showing anembodiment (8) of the method or the mode of connecting oxidesuperconducting wires according to the present invention.

FIG. 5 is a longitudinal sectional view schematically showing anembodiment (9) of the method or the mode of connecting oxidesuperconducting wires according to the present invention.

FIG. 6 is a longitudinal sectional view schematically showing anembodiment (10) of the method or the mode of connecting oxidesuperconducting wires according to the present invention.

FIG. 7 is a longitudinal sectional view schematically showing anembodiment (11) of the method or the mode of connecting oxidesuperconducting wires according to the present invention.

FIG. 8 is a longitudinal sectional view schematically showing anembodiment (12) of the method or the mode of connecting oxidesuperconducting wires according to the present invention.

FIG. 9 is a longitudinal sectional view schematically showing anembodiment (13) of the method or the mode of connecting oxidesuperconducting wires according to the present invention.

FIG. 10 is a longitudinal sectional view schematically showing anembodiment (17) of the method or the mode of connecting oxidesuperconducting wires according to the present invention.

FIG. 11 is a longitudinal sectional view schematically showing anembodiment (18) of the method or the mode of connecting oxidesuperconducting wires according to the present invention.

FIG. 12 is a longitudinal sectional view schematically showing anembodiment (20) of the method or the mode of connecting oxidesuperconducting wires according to the present invention.

FIG. 13 is a longitudinal sectional view schematically showing anembodiment (21) of the method or the mode of connecting oxidesuperconducting wires according to the present invention.

FIG. 14 is a diagram conceptually showing an apparatus for performing abending strain test of connectional wires in Examples 1 and 2.

FIG. 15 illustrates the relation between the ratio Ic/IcO between acritical current Ic and an initial critical current IcO of eachconnectional wire after the bending strain test in Example 2 and thetotal number of pulleys passed by each connectional wire in the bendingstrain test.

FIG. 16 illustrates current (I)-voltage (E) characteristics measured asto a connectional wire d in Example 2.

BEST MODES FOR CARRYING OUT THE INVENTION

The following various embodiments can be listed as the method or themode of connecting oxide superconducting wires according to the presentinvention. The respective embodiments are now described with referenceto drawings.

FIGS. 1, 4 and 6 to 12 are longitudinal sectional views schematicallyshowing various embodiments of the method or the mode of connectingoxide superconducting wires according to the present invention. FIGS. 2,3, 5 and 13 are plan views schematically showing various embodiments ofthe method or the mode of connecting oxide superconducting wiresaccording to the present invention.

(1) As shown in FIG. 1, end portions of tape-like or round bismuth oxidesuperconducting wires 1 and 2 are superposed and bonded with each other.A brazing filler metal 3 consisting of a material such as lead-tin alloysolder containing silver is arranged between the end portions of theoxide superconducting wires 1 and 2. Thus, the two oxide superconductingwires 1 and 2 are connected with each other. According to thisembodiment, the length of a junction L is set to at least one time andnot more than 100 times the diameter or the width of the oxidesuperconducting wires 1 and 2. Thus, the quantity of strain on an end ofthe junction can be reduced to be close to the quantity of strain onnon-superposed portions of the wires when the wires connected with eachother are bent.

(2) In the connection mode shown in FIG. 1, wide surfaces of the oxidesuperconducting wires 1 and 2 having rectangular cross sections aresuperposed to be bonded with each other. Thus, the quantity of strain onan end of the junction is reduced when the wires connected with eachother are bent.

(3) In the connection mode shown in FIG. 1, the thickness t of thebrazing filler metal 3 is set to be qt least 0.01 times and not morethan one time the diameter D or the thickness T of the oxidesuperconducting wires 1 and 2. Thus, the quantity of strain on an end ofthe junction can be reduced when the wires connected with each other arebent.

(4) In the connection mode shown in FIG. 1, the ribbon-like brazingfiller metal 3 is held between the end portions of the oxidesuperconducting wires 1 and 2 having rectangular cross sections andheated thereby bonding the oxide superconducting wires 1 and 2 to eachother.

(5) End portions of round oxide superconducting wires 1 and 2 aretwisted and superposed, and bonded with each other with interposition ofa brazing filler metal 3 therebetween.

(6) The oxide superconducting wires 1 and 2 are bonded to each other sothat the pitch of the aforementioned twisting is at least one time andnot more than 10 times the diameter of the wires 1 and 2.

(7) As shown in FIG. 2 or 3, an end portion 11 a or 11 b of an oxidesuperconducting wire 1 is so worked that the diameter D (in the case ofa round wire) or the width W (in the case of a tape-like wire) isreduced toward the end in a plane shape. An end portion 21 a or 21 b ofanother oxide superconducting wire 2 is also worked similarly to theabove. Thus, the quantity of strain on an end of a junction can bereduced when the wires connected with each other are bent.

In the connection mode shown in FIG. 2, the ends of the wires are so cutthat the end portions 11 a and 21 a have V shapes in the case of thetape-like wire. In the connection mode shown in FIG. 3, the ends of thewires are so cut that the end portions 11 b and 21 b have end surfacesinclined in the width direction across the widths of the tape-like wiresin the case of the tape-like wires.

(8) As shown in FIG. 4, an end portion 12 of an oxide superconductingwire 1 and an end portion 22 of another oxide superconducting wire 2 areso worked that the thickness T of the wires is reduced toward the ends.Thus, the quantity of strain on an end of a junction can be reduced whenthe wires connected with each other are bent.

(9) As shown in FIG. 5, notches are formed on an end portion 13 of anoxide superconducting wire 1 and an end portion 23 of another oxidesuperconducting wire 2. The diameter (in the case of round wires) or thewidth (in the case of tape-like wires) of the notches is increasedtoward the ends. Thus, the quantity of strain on an end of a junction isreduced when the wires connected with each other are bent.

(10) As shown in FIG. 6, a brazing filler metal 3 is arranged partiallyalong superposed end portions of oxide superconducting wires 1 and 2while defining spaces 31 and 32. When a junction is bent in the modeshown in FIG. 6, the end portion of one of the wires pushes back thesurface of the other wire in each of the spaces 31 and 32 therebyrelaxing concentration of strain. Thus, the quantity of strain on an endof the junction is reduced when the wires connected with each other arebent.

(11) As shown in FIG. 7, a junction between ends of oxidesuperconducting wires 1 and 2 is partially coated with flexiblematerials 41.

(12) As shown in FIG. 8, a junction between ends of oxidesuperconducting wires 1 and 2 is entirely coated with flexible materials41.

Thus, the quantity of strain on an end of the junction can be reducedwhen the wires connected with each other are bent.

(13) As shown in FIG. 9, a junction between oxide superconducting wires1 and 2 is partially or entirely coated with tape-like materials 42consisting of polyimide, copper, silver or the like.

(14) In the connection mode shown in FIG. 7 or 8, materials 41 ofpolyvinyl formal (PVF) resin or epoxy resin are employed. In this case,the aforementioned organic substance is partially or entirely applied tothe junction and dried thereby partially or entirely coating thejunction.

(15) In the connection mode shown in FIG. 9, metal tapes are employed asthe materials 42 and the metal tapes are entirely or partially brazed tothe junction thereby forming coatings.

(16) In the connection mode shown in FIG. 7 or 8, brazing filler metalsare employed as the materials 41 and partially or entirely brazed to thejunction thereby forming coatings. In this case, it is preferable toemploy solder consisting of a lead-tin alloy containing silver having ahigh melting point as the material for the brazing filler metal 3, andto employ indium-based solder having a low melting point as thematerials 41 forming the coatings. Thus, the junction can be coated withthe materials 41 consisting of solder having a relatively low meltingpoint after bonding the wires 1 and 2 with each other through thebrazing filler metal 3.

(17) As shown in FIG. 10, a junction between oxide superconducting wires1 and 2 is inserted into a material 43 having an annular shape to beentirely coated, and subjected to shrinkage fitting thereby forming acoating. Alternatively, a material 43 consisting of an organic substancehaving an annular shape coating the junction in place of a metal may beemployed and shrunk by heating thereby forming a coating. Aheat-shrinkable tube may be employed as the material 43 having anannular shape.

(18) As shown in FIG. 11, a junction may be partially inserted intomaterials 44 consisting of a metal or an organic substance havingannular shapes to be partially coated, and subjected to shrinkagefitting or heat-shrinking to be formed with coatings.

When the junction is partially or entirely coated as described above,the quantity of strain on an end of the junction can be reduced when thewires connected with each other are bent.

(19) In each of the connection modes described in the above items (11)to (18), the junction may be first partially or entirely coated with amaterial consisting of a metal, so that a material consisting of anorganic substance is thereafter arranged thereon for forming a coating.

(20) As shown in FIG. 12, an end of a wire is coated with a material 45consisting of a metal or an organic substance in a junction betweenoxide superconducting wires 1 and 2. In this case, the thickness of thematerial 45 forming a coating is set to be reduced as separated from thejunction. Thus, the quantity of strain on an end of the junction can bereduced when the wires connected with each other are bent.

(21) As shown in FIG. 13, the width of a material 46 consisting of ametal or an organic substance coating an end of a wire on a junctionbetween oxide superconducting wires 1 and 2 is set to be narrowed asseparated from the junction. Also in this case, the quantity of strainon an end of the junction can be reduced when the wires connected witheach other are bent.

EXAMPLE 1

Three connectional wires were prepared by connecting bismuth-based(Bi(Pb)—Sr—Ca—Cu—O-based) oxide superconducting wires with solderconsisting of a lead-tin alloy containing silver. Each wire was preparedfrom a tape-like wire obtained by coating 61 bismuth-based oxidesuperconductor filaments with a silver alloy sheath containing 0.3percent by weight of manganese. The tape-like wire was 0.24 mm inthickness, 3.8 mm in width and 300 mm in length. The length L (seeFIG. 1) of a junction between such wires was 100 mm. A voltage definedas 1 μV/cm was applied to each of the three connectional wires with aninter-terminal distance of 200 mm including the junction for measuring acritical current Ic, which was 55 A in each connectional wire.

The three connectional wires were worked as follows:

-   -   (a) Connectional Wire a Not worked but left in the connection        mode shown in FIG. 1.    -   (b) Connectional Wire b

Coatings 41 were formed by applying polyvinyl formal (PVF) resin toentirely coat the junction of the connectional wire and drying the sameas shown in FIG. 7.

-   -   (c) Connectional Wire c

Polyimide tapes 42 were bonded to coat the junction as shown in FIG. 9.

A test of applying bending strain to each of the aforementionedconnectional wires a, b and c was executed. The bending strain test wasperformed by alternately bringing a surface and an opposite surface ofthe connectional wire into contact with outer peripheral areas of guiderollers (pulleys) of 180 mm in outer diameter over a central angle ofabout 180° and moving the same by five turns respectively in a statelongitudinally applying tension 5N to the connectional wire, as shown inFIG. 14. Thus, the bending strain test was performed on the assumptionof conditions close to those of an actual winding step passed through anumber of pulleys, in order to verify mechanical strength of theconnected portion. After the bending strain test, the critical currentIc was measured as to each of the connectional wires a, b and a.Consequently, the connectional wire a exhibited a value 30 A lower thanan initial critical current 55 A while the connectional wire b and theconnectional wire c exhibited high critical currents 48 A and 50 Arespectively, and such results were obtained that the critical currentscan be maintained at high ratios with respect to initial criticalcurrents.

EXAMPLE 2

Four connectional wires were prepared by connecting bismuth-based(Bi(Pb)—Sr—Ca—Cu—O-based) oxide superconducting wires with solderconsisting of a lead-tin alloy containing silver. Each wire was preparedfrom a tape-like wire obtained by coating 61 bismuth-based oxidesuperconductor filaments with a silver alloy sheath containing 0.3percent by weight of manganese. Wide surfaces of such tape-like wireswere superposed to be bonded with each other. The tape-like wire was0.24 mm in thickness, 3.8 mm in width and 300 mm in length. The length L(see FIG. 1) of a junction between such wires was 50 mm. Voltageapplication terminals were mounted about the junction at aninter-terminal distance of 100 mm for applying a voltage defined as 1μV/cm to each of the four connectional wires from these voltageapplication terminals and measuring a critical current IcO (initialcritical current), which was 60 A in each connectional wire.

These four connectional wires were worked as follows:

-   -   (d) Connectional Wire d

Ends of two tape-like wires were cut (V-cut) into V shapes as shown inFIG. 2 and wide surfaces of the tape-like wires were superposed andbonded with each other, while lengths La and Lb were set to 40 mm and 5mm respectively.

-   -   (e) Connectional Wire e

Ends of two tape-like wires were cut (N-cut) so that the ends had endsurfaces inclined along the width direction across the widths of thetape-like wires as shown in FIG. 3 and wide surfaces of the tape-likewires were superposed and bonded with each other, while lengths La andLb were set to 40 mm and 5 mm respectively.

-   -   (f) Connectional Wire f

Wide surfaces of two tape-like wires were superposed and bonded witheach other without cutting ends of the tape-like wires as shown in FIG.10, thereafter the junction (length L: 50 mm) was inserted into aheat-shrinkable tube having a length Lc of 60 mm and a thickness of 0.15mm before shrinkage to be entirely coated, and the tube was shrunk byheating at about 100° C. for forming a coating. Electron-bridged softflame-retarded polyolefin resin was employed as the material for theheat-shrinkable tube.

-   -   (g) Connectional Wire g

Not worked but left in the connection mode shown in FIG. 1.

A test of applying bending strain to each of the aforementionedconnectional wires d, e, f and g was executed. The bending strain testwas performed by alternately bringing a surface and an opposite surfaceof the connectional wire into contact with outer peripheral areas ofguide rollers (pulleys) of 200 mm in outer diameter over a central angleof about 180° and moving the connectional wire to pass through the guiderollers in a state longitudinally applying tension 5N to theconnectional wire, as shown in FIG. 14. Thus, the bending strain testwas performed on the assumption of conditions close to those of anactual winding step passed through a number of pulleys, in order toverify mechanical strength of the connected portion. After the bendingstrain test, the critical current Ic was measured as to each of theconnectional wires d, e, f and g.

FIG. 15 shows the relation between the ratio Ic/IcO of the criticalcurrent Ic to the initial critical current IcO of each connectional wireafter the bending strain test and the total number of the pulleys passedby each connectional wire in the bending strain test. It is understoodfrom FIG. 15 that the ratios of reduction of the critical currents Icafter the bending strain test were smaller in the connectional wires d,e and f having worked junctions as compared with the connectional wire ghaving a non-worked junction.

FIG. 16 shows current (I)-voltage (E) characteristics measured as to theconnectional wire d. Referring to FIG. 16, a curve “not bent” shows dataof the connectional wire d not subjected to bending strain, and curves“500 g, φ200×10 times”, “500 g, φ200×20 times” and “500 g, φ200×30times” show data of the connectional wire d passed through the guiderollers of 200 mm in outer diameter 10 times, 20 times and 30 timesrespectively with application of a load of 500 g to be subjected totensile bending strain. Referring to FIG. 16, inclination of thecurrent-voltage characteristic curves with reference to a current I of 0to 40 A shows connection resistance of the wire. It is understood fromFIG. 16 that the inclination remains substantially unchanged in eachcurve and hence constant connection resistance was maintained also afterapplication of the tensile bending strain and the connection resistanceas well as the critical current Ic were hardly deteriorated. It is alsounderstood that the connection resistance was about 20 nΩ.

Embodiments and Examples disclosed above are illustratively shown in allpoints, and to be considered as not restrictive. The scope of thepresent invention is shown not by the aforementioned embodiments andExamples but by the scope of claim for patent, and to be interpreted asincluding all exemplary corrections and modifications within the meaningand range equivalent to the scope of claim for patent.

INDUSTRIAL APPLICABILITY

The oxide superconducting wire or the superconducting coil according tothe present invention is suitably employed for superconductingapparatuses such as a superconducting transformer, a superconductingcurrent limiter and a magnetic field generator employing superconductingmagnets. Further, the oxide superconducting wire according to thepresent invention is suitably employed for superconducting apparatusessuch as a superconducting cable and a superconducting bus bar. Inaddition, the method of manufacturing an oxide superconducting wireaccording to the present invention is applicable for manufacturing thesesuperconducting apparatuses.

1. An oxide superconducting wire comprising: a first oxidesuperconducting wire having a first end portion; a second oxidesuperconducting wire having a second end portion; and said first oxidewire comprising at least a first superconducting filament surrounded byand in direct contact with a first sheath at least at said first endportion; said second oxide wire comprising at least a secondsuperconducting filament surrounded by and in direct contact with asecond sheath at least at said second end portion; said first oxidesuperconducting wire including a first outer surface defined by an outersurface of said first sheath and a first edge surface defined by an endof said first superconducting filament and an end of said first sheath;said second oxide superconducting wire including a second outer surfacedefined by an outer surface of said second sheath and a second edgesurface defined by an end of said second superconducting filament and anend of said second sheath; said first outer surface forming a junctionwith said second outer surface by connecting said first outer surface tosaid second outer surface, in a region of said first and second endportions, by a brazing filler metal disposed therebetween; and saidfirst edge surface being displaced from said second edge surfacelongitudinally along the direction of said first and secondsuperconducting wires.
 2. The oxide superconducting wire according toclaim 1, wherein said oxide superconducting wires are tape-shaped wireshaving rectangular cross sections.
 3. The oxide superconducting wireaccording to claim 2, wherein said junction includes a junction formedby superposing wide surfaces of two said tape-shaped wires.
 4. The oxidesuperconducting wire according to claim 3, wherein at least one of saidend portions is so worked that the width (W) of said at least one ofsaid end portions is reduced toward the end.
 5. The oxidesuperconducting wire according to claim 4, wherein said junction (L)includes an end portion having a V shape in plane.
 6. The oxidesuperconducting wire according to claim 3, wherein at least one of saidend portions is so worked that the thicknesses of said at least one ofsaid end portions is reduced toward the distal end thereof.
 7. The oxidesuperconducting wire according to claim 1, wherein said junction is atleast partially coated with a metal or an organic substance.
 8. Theoxide superconducting wire according to claim 7, wherein said junctionis at least partially inserted into a material having an annular shape.9. The oxide superconducting wire according to claim 1, wherein saidoxide superconducting wires contain a bismuth oxide superconductor. 10.The oxide superconducting wire according to claim 9, wherein saidbismuth oxide superconductor is a filament coated with a materialcontaining silver.